GTPv2 sessions are started by a sender, such as an MME or PGW, sending a create session request over the S11 or S5/S8 interface to a receiver such as an SGW or PGW. The create session request message contains all of the IEs that the nodes require to establish the session.

Sent by a node in response to a create session request message. Create session responses include IEs required to establish the session. In addition, the create session response also indicates whether the sender can accept the request (for example, by including Request accepted or Request accepted partially) or not (for example, by including a description of the cause of the failure, for example, Missing or unknown APN).

This multi-purpose message can be used for a number of purposes, for example:

• On the S5/S8 interface from the PGW to the SGW or on the S11 interface from the SGW to the MME during dedicated bearer activation.
• On the S5/S8 interface from the PGW to the SGW or on the S4 interface from the SGW to the SGSN during of secondary PDP context activation or network requested secondary PDP context activation.
• On the S2a interface from the PGW to the TWAN as part of dedicated bearer activation in WLAN on GTP S2a or on the S2b interface from the PGW to the ePDG during dedicated S2b bearer activation with GTP on S2b.
• On the S5/S8 or S2a/S2b interface from the PGW to the SGW or from the TWAN/ePDG or on the S11/S4 interface from the SGW to the MME/S4-SGSN during Network-initiated IP flow mobility or UE-initiated IP flow mobility.

Sent by a node in response to a create bearer request message. Create bearer responses include IEs required to respond to the create bearer request. In addition, the create bearer response also indicates whether the sender can accept the request (for example, by including Request accepted or Request accepted partially) or not (for example, by including a description of the cause of the failure, for example, Semantic error in the TFT operation).

Sent from an MME to a SGW and forwarded to the PGW during the UE requested bearer resource allocation or UE requested bearer resource modification. These operations are also used for dedicated bearer activation and deactivation.

Also sent on the S4 interface from a SGSN to a SGW and on the S5/S8 interface from a SGW to a PGW during MS-initiated PDP context modification, or secondary PDP context activation.

Also sent on the S11/S4 interface from an MME/S4-SGSN to a SGW and on the S5/S8 or S2a/S2b interface from a SGW or from a TWAN/ePDG to a PGW during UE-initiated IP flow mobility and UE requested IP flow mapping.

Sent by a node in response to a bearer resource command message to indicate a failure. Bearer resource failure indications include IEs required to respond to the command.The response also indicates the reason for the failure (for example, by including Semantic errors in packet filtery).

This multi-purpose is sent as part of many processes to request changes or updates to processes or data.

Sent by a node in response to a modify bearer request command message to respond to the request. Modify bearer responses include IEs required to respond to the modify bearer request. In addition, the modify bearer response also indicates whether the sender can accept the request (for example, by including Request accepted or Request accepted partially) or not (for example, Service not supported).

Sent in many different instances to end sessions or delete bearer resources in response to errors or changes in status or because sessions have ended.

Sent by a node in response to a delete session request or delete bearer request command message to respond to the request. The response messages include IEs to acknowledge that the delete request has been responded to.

Sent by nodes to notify downstream nodes to expect downlink data. Receiving nodes can use downlink data notification acknowledge messages to indicate if the node can fail or succeed in responding to the request. The downlink data notification failure is sent if a node can respond to the initial request but a failure occurs during the downlink operation.

Sent on the S4/S11 interface by the SGSN/MME to the SGW to delete indirect forwarding tunnels in source SGW/Target SGWs.

Sent on the S4/S11 interface by SGWs to SGSNs/MMEs as part of a variety of processes such as S1-based handovers, UTRAN Iu mode to E-UTRAN Inter RAT handovers, and so on.

Sent over the S11 interface from the MME to the SGW or over the S5/S8 interface from the SGW to the PGW during HSS initiated subscribed QoS modification, or when the SQCI flag or the PSCI flag is set to 1 in the context response message.

Also sent over the S4 interface by the SGSN to the SGW or over the S5/S8 interface from the SGW to the PGW during the HSS Initiated subscribed QoS modification procedure or when the SQCI flag or the PSCI flag is set to 1 in the context response message.

Also sent on the S2a/S2b interface from the TWAN/ePDG to the PGW as part of HSS initiated subscribed QoS modification.

The failure indication is sent back to the sender of the modify bearer command if the command fails.

Sent from the PGW to the SGW, TWAN/ePDG or from the SGW to the MME/S4-SGSN as part of a number of processes that update bearer QoS and other settings.

Sent in response to an update bearer request to verify whether the bearer has been successfully modified by the request or not.

Sent over the S11 interface from the MME to the SGW and over the S5/S8 interface from the SGW to the PGW during of the eNodeB requested bearer release or MME-initiated dedicated bearer deactivation.

Also sent over the S4 interface from the SGSN to the SGW and over the S5/S8 interface from the SGW to the PGW during MS and SGSN initiated bearer deactivation using S4.

The failure indication message is sent in response to the delete bearer command if the request fails, and includes information about the reason for the failure.

Sent on the S11/S4 interface by the MME/SGSN to the SGW during the handover or TAU/RAU procedure with serving GW change and data forwarding

Sent by the SGW to the MME/SGSN as a response to a create indirect data forwarding tunnel request message to indicate if the indirect data forwarding tunnel has been created in the SGW or not and why if not successful.

Sent on the S11 interface from the MME to the SGW during S1 release and eNodeB initiated connection suspend.

Also sent on the S11 interface from the MME to the SGW as part of the establishment of S1-U bearer during data transport in control plane CIoT EPS optimization procedure.

Also sent on the S4 interface from the SGSN to the SGW as part of the RAB release using S4, Iu Release using S4, or READY to STANDBY transition within the network.

Sent in response to release access bearers requests. The response indicates if the request is successful or not.

Sent over the S11/S4 interface from the SGW to the MME/SGSN as a part of a network triggered service request.

Sent from the MME to SGW if both the SGW and the MME support the MABR feature. An MME sends a modify access bearer request message on the S11 interface to an SGW as part of a number of different processes that modify bearers.

Sent in response to modify access bearers requests to indicate whether the request was successful or not.

Sent be from MME to SGW and from SGW to PGW to notify the SGW that at least one remote UE is newly connected to or disconnected from a ProSe UE-to-network relay.